This invention relates to polymerization cocatalyst compounds containing weakly coordinating Group-13 element anions and to the preparation of olefin polymers using catalyst systems based on organometallic transition-metal cationic compounds stabilized by these anions.
The term xe2x80x9cnoncoordinating anionxe2x80x9d (NCA) is now accepted terminology in the field of olefin and vinyl monomer, coordination, insertion, and carbocationic polymerization. See, for example, EP 0 277 003, EP 0 277 004, U.S. Pat. No. 5,198,401, U.S. Pat. No. 5,278,119, and Baird, Michael C., et al, J. Am. Chem. Soc. 1994, 116, 6435-6436. The noncoordinating anions are described to function as electronic stabilizing cocatalysts, or counterions, for essentially active, cationic metallocene polymerization catalysts. The term noncoordinating anion applies both to truly noncoordinating anions and to coordinating anions that are labile enough to undergo replacement by olefinically or acetylenically unsaturated monomers at the insertion site. These noncoordinating anions can be effectively introduced into a polymerization medium as Bronsted acid salts containing charge-balancing countercations, as ionic cocatalyst compounds, or mixed with an organometallic catalyst before adding it to the polymerization medium. See also, the review articles by S. H. Strauss, xe2x80x9cThe Search for Larger and More Weakly Coordinating Anionsxe2x80x9d, Chem. Rev., 93, 927-942 (1993).
U.S. Pat. No. 5,502,017, to Marks et al., addresses ionic metallocene polymerization catalysts for olefin polymerization containing a weakly coordinating anion comprising boron substituted with halogenated aryl substituents preferably containing silylalkyl substitution, such as tert-butyldimethyl-silyl. Marks et al. disclose the weakly coordinating anion as the cocatalyst. The silylalkyl substitution is said to increase the solubility and thermal stability of the resulting metallocene salts. Examples 3-5 describe synthesis of and polymerization with the cocatalyst compound triphenylcarbenium tetrakis (4-dimethyl-t-butylsilyl-2,3,5,6-tetrafluorophenyl)borate.
In view of the above, there is a continuing need for olefin polymerization activators both to improve the industrial economics of solution polymerization and to provide alternative activating compounds for ionic, olefin polymerization catalyst systems.
The invention provides anion-containing cocatalyst precursor compounds which can be combined with organometallic catalyst precursor compounds to form active olefin polymerization catalysts for insertion, coordination, or carbocationic polymerization. Olefin polymerization can proceed by catalyst formation followed by or in situ catalyst formation essentially concurrent with, contacting the catalyst with appropriate monomers: those having accessible, olefinic or acetylenic unsaturation or having olefinic unsaturation capable of cationic polymerization. The invention catalysts are suitable for preparing polymers and copolymers from olefinically and acetylenically unsaturated monomers. The anions [A]xe2x88x92 of the cocatalyst precursors are those containing a Group-13 element core to which fluoroaryl ligands are connected, at least one of these fluoroaryl ligands is substituted with a Group-15 element containing a lone-pair electron functionality.
Additionally, the Group-15 element is attached to an electron withdrawing ligand that causes the lone-pair to become essentially inert, i.e., it will not strongly coordinate to the activated catalyst.
Preferred invention cocatalyst precursor compounds can be represented by the following formula:
[Ct]+[M(ArF)n{(ArF)E(ArF)(R)}4xe2x88x92n)]xe2x88x92,
where [Ct]+ is a cation capable of abstracting an alkyl group, or breaking a carbon-metal connection, M is a Group-13 element, ArF is a fluorinated aryl group, E is a Group-15 element, n equals 0 to 3, and R is a C1-C20 hydrocarbyl or hydrocarbylsilyl substituent.